1. Field of Invention
The present invention relates to a method and apparatus for measuring position of object for vehicle by using optical radars.
2. Prior Art
Microwave or ultrasonic radar systems have been known to measure position of object for vehicle. A problem of such systems is interference from other radar systems where significant number of vehicles equipped with the same or similar radar systems are involved. Another disadvantage of such systems is that it is difficult to make an accurate measurement of distance to an object in short range. Optical radar systems using laser are well known. For example, U.S. Pat. No. 5,529,138 dated Jun. 25, 1996 and U.S. Pat. No. 5,177,462 dated Jan. 5, 1993 disclose the optical radar systems. In the optical radar systems, distance to an object is obtained by measuring a propagation time of light pulse between the vehicle and the object or by measuring a shift of image formed on image sensor. These systems also have the interference problem and the difficulty of measuring position of object in short range. Thus, it is an object of the present invention to provide a method and apparatus for measuring position of object, wherein the foregoing disadvantages are improved. The method and apparatus of the present invention easily avoids the interference from other vehicles equipped with the same systems and can accurately measure position of object in short range.
It is an object of the present invention to provide a method and apparatus for measuring position of object for vehicle.
In the first embodiment, a pair of two optical radar units separated by a distance is mounted at the rear side of the vehicle to detect objects behind the vehicle. Each optical radar unit can emit light pulses in a direction and receive light pulses coming from the same direction as the emitted light beam. The light beams of the two separate optical radar units are directed to a point. One of the two optical radar units, which is called the first optical radar unit, emits a light pulse to the point and the other, which is called the second optical radar unit, detects the light pulse reflected from the point. After a time interval, the second optical radar unit emits a light pulse to the point and the first optical radar unit detects the light pulse reflected from the point. If there is an object at the point, the time difference of the two signals detected by the two optical radar units is the switching time interval. Thus, by comparing the two detected signals, one can determine whether an object is at the point or not. A time delay circuit and a multiplier circuit can be used to compare the two detected signals. The time delay circuit delays the signal detected from the second optical radar unit by the switching time interval and in the multiplier circuit the signal detected from the first optical radar unit is multiplied by the delayed signal. The result of the multiplication is displayed at the position of the point on a display means. The position of the point is determined on the basis of the two directions of the light beams and the separation of the two optical radar units. By changing the directions of the two light beams, the optical radar units scan an area. This method easily avoids interference from other vehicles equipped with the same or similar optical radar units and accurately measures position of object in short range without using sophisticated means.
The second embodiment uses a plurality of optical radar units. This comprises two sets of optical radar units. Each set has four optical radar units. Two optical radar units are selected in the two sets to form a scanning point. There are sixteen possible combinations of optical radar units. The use of the plurality of optical radar units reduces time to scan an area and increases density of scanning points in the area.
The third embodiment uses at least one optical radar unit and at least one light detecting means separated by a distance. The light beams of the optical radar unit and the light detecting means are directed to a point. The optical radar unit emits a light pulse to the point and the optical radar unit and the light detecting means detect the light pulse reflected from the point at the same time. By comparing the two signals detected by the optical radar unit and the light detecting means, one can determine whether an object is at the point or not. The position of the point is determined on the basis of the two directions of the light beams and the separation of the optical radar unit and the light detecting means.
The method and apparatus of the present invention easily avoids interference from the vehicles equipped with the same systems and can accurately measure positions of objects in short range.